Classification: Hazard Classes, Divisions, Packing Groups, and Subsidiary Risks
The classification system
The IMDG Code recognises nine classes. Class 1 explosives has six divisions (1.1-1.6) and compatibility groups. Class 2 gases divides into 2.1 flammable, 2.2 non-flammable non-toxic, and 2.3 toxic. Class 3 flammable liquids, Class 4 divides into 4.1 flammable solids, 4.2 spontaneously combustible, and 4.3 dangerous when wet. Class 5 divides into 5.1 oxidising substances and 5.2 organic peroxides. Class 6 divides into 6.1 toxic and 6.2 infectious substances. Class 7 is radioactive, Class 8 corrosive, and Class 9 miscellaneous, which includes marine pollutants and environmentally hazardous substances. Packing groups apply to many classes: PG I great danger, PG II medium, PG III minor. Classes 1, 2, 5.2, 6.2 and 7 generally do not use packing groups.
Traps candidates fall into
- Assigning a packing group to a class that does not use them (e.g., Class 2 or Class 7).
- Confusing a subsidiary risk with the primary class. The primary class drives the label and the Dangerous Goods List entry; subsidiary risks add labels and segregation consequences.
- Missing that a substance can be a marine pollutant even when it is not otherwise dangerous; Class 9 covers this.
- Overlooking that the packing group affects the packing instruction and often the stowage category.
Worked example
A consignment is a flammable liquid with a toxic subsidiary risk. Primary class 3, subsidiary 6.1, packing group II. The entry in the Dangerous Goods List gives the UN number, proper shipping name, class, PG, packing instruction, stowage and segregation codes. The label shows Class 3 as primary and Class 6.1 as subsidiary; segregation must consider both.